This invention relates to a one-way clutch for effecting or blocking torque transmission between inner and outer rings by rocking motion of cam members according to a direction of relative rotation of the inner and outer rings, and more particularly relates to measures for reducing the speed at which the cam members slide on the inner ring.
As for example disclosed in Japanese Unexamined Patent Publication No. 61-228153, it is known that in an auxiliary equipment driving apparatus for transmitting torque of a crank shaft of a vehicle engine to a rotor of auxiliary equipment through a power transmission belt, a one-way clutch is disposed in a torque transmission path of the auxiliary equipment driving apparatus to absorb slight variations in angular velocity of torque, resulting from an explosion stroke of the engine, thereby reducing a load of the power transmission belt. Specifically, the one-way clutch operates to effect transmission of torque of the crank shaft to the rotor of the auxiliary equipment for a period of increase in angular velocity of the crank shaft during slight variations in angular velocity thereof, and block transmission of inertial torque of the rotor to the crank shaft for a period of decrease in angular velocity of the crank shaft during slight variations in angular velocity thereof. In particular, if the auxiliary equipment is an alternator, its rotor has large inertial torque and therefore the effect of reducing a belt load is significant.
Now, description will be made about a conventional one-way clutch with reference to exemplary one-way clutch-integrated pulleys each formed by building a one-way clutch into a pulley. Such one-way clutch-integrated pulleys include two known types: a first type of relatively rotatably supporting inner and outer rings b, c to a single bearing a as shown in FIG. 13; and a second type of relatively rotatably supporting inner and outer rings b, c to axially juxtaposed two bearings a, a as shown in FIG. 14. In either type, the bearing a is juxtaposed with a clutch mechanism f formed by retaining a plurality of sprags d, d, . . . as cam members in a cage e to allow their tilting motion therein.
For the period of increase in angular velocity of the crank shaft during slight variations in angular velocity thereof, when the outer ring c relatively rotates in its locking direction (clockwise in FIG. 15), each sprag d of the clutch mechanism f tilts clockwise in FIG. 15 to wedge between the inner and outer rings b, c, thereby effecting torque transmission between the inner and outer rings b, c. On the other hand, for the period of decrease in angular velocity of the crank shaft during slight variations in angular velocity thereof, when the outer ring c relatively rotates in its unlocking direction (counterclockwise in FIG. 15), each sprag d tilts opposite to the direction to wedge between the rings, i.e., counterclockwise in FIG. 15, to slide on the inner and outer rings b, c so that the inner and outer rings b, c idle, thereby blocking torque transmission between the inner and outer rings b, c. To implement such behaviors, surfaces of each sprag d in contact with cam surfaces of the inner and outer rings b, c are formed into cam surfaces so as to change the tilting direction of the sprag d depending upon the direction of relative rotation of the inner and outer rings b, c.
In such a conventional one-way clutch using sprags as cam members, however, the actual sprags d, d, . . . do not produce equal sliding motions between the inner and outer rings b, c during idling (relative rotation in the unlocking direction) of the inner and outer rings b, c. More specifically, when the speed of relative rotation of the outer ring c with respect to the inner ring b is indicated by V1 and the speed of relative bodily movement of each sprag d around the inner ring b is indicated by V2, the relationship of V1=V2 is established. Accordingly, each sprag d slides only on the inner ring b which is a member with small resistance to torque.
Therefore, under service conditions of a large number of idlingmovements, for example, in sucha case as used in an auxiliary equipment driving apparatus for vehicle engines which frequently perform quick speed-up and speed-down running within the high engine speed range, abrasion is caused excessively on the cam surface of each sprag d in contact with the inner ring b over the other portions thereof. Therefore, abrasion is also likely to progress on the cam surface of the inner ring b. As a result of these phenomena, functional durability of the clutch will be readily deteriorated.
A principal object of the present invention is, in a one-way clutch for connecting and disconnecting torque transmission between inner and outer rings by rocking cam members in a clutch mechanism when the inner and outer rings relatively rotates via a bearing, to obviate excessive abrasion only on the cam surface of each cam member in contact with the cam surface of the inner ring and progressive abrasion on the cam surface of the inner ring by sliding each cam member also on the outer ring and reducing the speed of slid of each cam member on the inner ring during idling of the inner and outer rings, with the use of rotational movement of a cage of the bearing, resulting in improved functional durability of the clutch.
To attain the above object, the inventors direct their attention to the bearing cage relatively rotating in the same direction as that of relative rotation of the outer ring at a lower relative rotational speed than that of the outer ring, and aim at sliding each cam member also on the outer ring to reduce the speed of slide of each cam member on the inner ring by connecting the cage of the bearing to the cage of the clutch mechanism to make the speed of relative bodily movement of each cam member around the inner ring slower than the relative rotational speed of the outer ring.
More specifically, the present invention is directed to a one-way clutch comprising: an inner ring; an outer ring which is coaxially disposed around the inner ring and relatively rotatably assembled with the inner ring; a bearing having a plurality of rolling elements arranged for rolling motion between the inner and outer rings in a plane orthogonal to a rotational axis of the inner and outer rings and a cage, disposed between the inner and outer rings for rotation around the rotational axis of the inner and outer rings, for retaining the plurality of rolling elements to allow their rolling motion, the bearing relatively rotatably supporting the inner and outer rings so that the plurality of rolling elements roll to rotate the cage in the same direction as that of relative rotation of the outer ring at a lower relative rotational speed than that of the outer ring; and a clutch mechanism having a plurality of cam members arranged for rocking motion between the inner and outer rings in a plane orthogonal to the rotational axis of the inner and outer rings but different from the plane in which the rolling elements of the bearing are arranged and a cage, disposed between the inner and outer rings for rotation around the rotational axis of the inner and outer rings, for retaining the plurality of cam members to allow their rocking motion, the clutch mechanism effecting torque transmission between the inner and outer rings by tilting motion of the plurality of cam members in a direction to wedge between the inner and outer rings during relative rotation of the inner and outer rings in their locking direction and blocking the torque transmission by tilting motion of the plurality of cam members opposite to the direction to wedge between the inner and outer rings during relative rotation of the inner and outer rings in their unlocking direction.
Further, the cage of the clutch mechanism is connected in unitarily rotating relation with the cage of the bearing.
With the above construction, the inner and outer rings of the one-way clutch are relatively rotatably supported to the bearing with the rolling elements of the bearing retained for rolling motion by the cage between the inner and outer rings. When torque is input into the one-way clutch so that the inner and outer rings are relatively rotated, each cam member of the clutch mechanism rocks in normal or reverse directions depending upon the direction of relative rotation of the inner and outer rings to effect or block torque transmission between the inner and outer rings. In other words, during relative rotation of the inner and outer rings in the locking direction, each cam member tilts in a direction to wedge between the inner and outer rings to effect torque transmission therebetween. In contrast, during relative rotation of the inner and outer rings in the unlocking direction, each cam member tilts opposite to the direction to wedge between the inner and outer rings to idle them thereby blocking the torque transmission therebetween.
When each cam member tilts opposite to the direction to wedge between both the rings during relative rotation of both the rings in the unlocking direction, the relative rotation of both the rings creates resistance against torque between each cam member and the inner ring and between each cam member and the outer ring. In such a case, since the resistance against torque created between each cam member and the inner ring is smaller than that created between each cam member and the outer ring, each cam member may tend to slide only on the inner ring, i.e., bodily move around the inner ring at substantially the same speed as the relative rotational speed of the outer ring.
With this construction, however, the rolling elements of the bearing roll to rotate the cage of the bearing in the same direction as that of relative rotation of the outer ring at a relative rotational speed lower than that of the outer ring. Therefore, each cam member in the clutch mechanism is forced by the cage of the clutch mechanism to bodily move around the outer ring opposite to the direction of relative rotation of the outer ring, i.e., in a direction to reduce the relative rotational speed of the outer ring. As a result, each cam member slides also on the outer ring and the speed of slide of each cam member on the inner ring is reduced. Therefore, Instead of abrasion of each cam member due to slide only on the inner ring, each cam member abrades due to slide on both the inner and outer rings. This obviates excessive abrasion of each cam member in its cam surface in contact with the inner ring during idling of the inner and outer rings and ease of progressive abrasion of the cam surf ace of the inner ring, thereby improving functional durability of the clutch.
In the above construction, the one-way clutch may include a pair of bearings, the pair of bearings may be arranged on both axially lateral sides of the clutch mechanism, respectively, and the cage of the clutch mechanism may be connected in unitarily rotating relation with at least one of the cages of both the bearings.
With this structure, during relative rotation of the inner and outer rings in the unlocking direction, the cage of the clutch mechanism rotates unitarily with at least one of the cages of both the bearings. Accordingly, the same effects and operations can be attained.
The one-way clutch may be disposed in a torque transmission path for transmitting torque of a crank shaft rotating with slight variations in angular velocity resulting from an explosion stroke of a vehicle engine to an input shaft of auxiliary equipment through a power transmission belt.
With this structure, the crank shaft of the vehicle engine rotates with slight variations in angular velocity resulting from the explosion stroke of the engine. For a period of increase in angular velocity of the crank shaft during slight variations in angular velocity thereof, the one-way clutch transmits torque of the crank shaft to the input shaft of the auxiliary equipment. On the other hand, for a period of decrease in angular velocity of the crank shaft during slight variations in angular velocity thereof, the one-way clutch blocks torque transmission between the crank shaft and the auxiliary equipment to avoid inertial torque of the rotor of the auxiliary equipment from being transmitted to the crank shaft.
In the above structure, the inner ring is preferably connected to either the crank shaft of the vehicle engine or the input shaft of the auxiliary equipment, and the outer ring is preferably provided in unitarily rotating relation with a pulley section for training the power transmission belt therearound.
With this structure, the pulley section for training the power transmission belt therearound is provided around the outer periphery of the outer ring of the one-way clutch, thereby forming a one-way clutch-integrated pulley. Therefore, when the one-way clutch-integrated pulley is carried on, for example, the input shaft of the auxiliary equipment, a torque transmission path is established between the crank shaft of the engine and the input shaft of the auxiliary equipment through the power transmission belt. Accordingly, the above effects and operations can be well achieved.